This invention relates to the field of circuit breakers. More particularly, this invention relates to the field of rating plugs for circuit breakers having electronic sensors or trip units.
Rating plugs for circuit breakers with electronic trip units are known in the art. The rating plug changes the operating curve for actuation of a breaker having an electronic circuit interrupter (trip unit), thus changing the ampere rating of the breaker. Not all rating plugs are compatible with all electronic trip units. Therefore, a known problem is to ensure that a rating plug is compatible with the electronic trip unit into which it is to be inserted.
For safety""s sake, all electronic trip units with interchangeable rating plugs are required to reject incorrect combinations of rating plugs and trip units. This rejection is typically accomplished by the insertion of pins into the receptacle in the trip unit into which the rating plug is to be inserted. The pins, which are inserted into the side of the trip unit housing, interfere with protrusions on the side of the rating plug housing.
While workable, this prior art system has several drawbacks or disadvantages. One of these is that the interference between pins and protrusions does not occur until the rating plug is almost fully inserted into the trip unit. This can result in the user mistakenly thinking that insertion of the rating plug has been properly completed. Another problem is that the pins are independent elements, i.e., they are not part of the rating plug housing or the trip unit housing. As a result, a pin can be removed by someone tampering with the unit, and the user will not know whether a pin should be present or not.
In an exemplary embodiment of the invention, an improved rating plug housing for a circuit breaker includes a recess formed in a portion of the circuit breaker housing. The recess has a projection formed on a bottom surface thereof. A rating plug, having an electronic portion arranged within a rating plug housing, is sized and shaped to fit into said recess. A tab extends from a bottom surface of said rating plug housing, said tab being arranged to contact said projection when said electronic portion is incompatible with a trip unit within said circuit breaker housing. If an attempt is made to insert an inappropriate rating plug into the circuit breaker housing, the tab on the rating plug unit will come into contact and interfere with the projection in the recess of the circuit breaker housing, and installation of the inappropriate rating plug will be prevented.